I use a split for ac only - installed last year (2020) I already had a shop furnace so just needed. ac. The shop is 24 x 36 with 10' ceilings and is fully insulated. I keep it around 70 degrees but only have to turn the ac on around July as the shop stays cool until then. I rarely open the large doors because everything in the shop is cool enough that it will immediately form dew from the humidity entering the shop. What doesn't rust will get moldy. I'm in the same weather belt as you.